Heretofore, an automatic transmission oil, that is, a lubricating oil for an automatic transmission, has been employed for assisting smooth operation of automatic transmission equipped with a torque converter, gear mechanism, wet clutch and hydraulic system, examples of such are automatic transmissions, continuously variable transmissions and dual clutch transmissions. In more recently developed automobiles, an increased focus is to increase performance and maintain improvements in fuel economy. In this regard, continuous research and improvement have been made in overall design and weight, component design and maximizing benefits from improved lubrication: particularly with respect to reduced friction and wear. Therefore, the recently developed automobiles have been manufactured to have a less volume and a less weight. The automatic transmissions are also required to be smaller sized, typically with smaller oil sumps, which operate under more severe conditions with higher torque capacity resulting in gear bearings receiving increased load or operating under higher speed rotations (6-speed AT). Even with more severe operating requirements, the lubricating oil is expected to maintain frictional characteristics with respect to the transmission clutches and minimize losses through the torque converter, thus improving of fuel economy. These, smaller sized and lighter weight automatic transmissions require a lubricating oil showing improved friction performance such as higher friction coefficient. In addition, since automobiles equipped with an automatic transmission sometimes encounter vibration (that is named “shudder”) when the automatic transmission operates, the lubricating oil is required to decrease the shudder caused in the operation of the automatic transmission for a sufficiently long period of time. In addition, continuously variable transmissions (CVT) commonly transmit engine torques by steel pulleys and a steel V-belt or chain, thus lubricants for these apparatus require a high metal friction coefficient.
WO 97/14773 A1 discloses a lubricating fluid for power transmissions which contains an additive comprising an alkenyl-substituted succinimide that is prepared by reaction of a succinic anhydride substituted with an alkenyl group having a branch structure in β-position and polyamine. It is described that the addition of the additive enables to maintain good anti-shudder performance for a long period of time.
WO 97/14772 A1 discloses a lubricating oil composition containing an alkenyl-substituted succinimide that is prepared by reaction of a succinic anhydride substituted with an alkenyl group having a branch structure in α-position and an amine compound.
WO 2008/157467 A2 discloses novel pyrrolidine compounds and succinimide compound which are of value as friction modifiers for imparting excellent friction modifying performance to lubricating oil compositions without adverse effects on the viscosity properties of the lubricating oil composition at low temperatures.
Tribology Online, Japanese Society of Tribologists, 3, 6 (2008), pp. 328-332 discloses results of studies of low molecular weight alkenyl succinimides on anti-shudder performance. In the study, a number of low molecular weight alkenyl succinimides and aliphatic amide compounds are tested. Examples of the low molecular weight alkenyl succinimides include a bis-type alkenyl-substituted succinimide obtained by reaction of succinic anhydride which is substituted with 2-pentyl-2-tridecyl and an amine compound as well as a bis-type alkenyl-substituted succinimide obtained by reaction of succinic anhydride which is substituted with 2-hexyl-2-hexadecenyl and an amine compound.